The present invention relates to a semiconductor integrated circuit device and, more particularly, to technology which is effectively applied in a semiconductor integrated circuit device including nonvolatile storage elements of a single layer polysilicon gate structure.
An example of a mask ROM (Read Only Memory), in which data are written using a mask, is disclosed in U.S. Pat. No. 4,939,386. Since this type of mask ROM can be fabricated by a poly-Si (polysilicon) one-layer process and is capable of storing one bit in one transistor, it is suitable for achieving larger capacity at lower cost. As mask ROMs are becoming more and more miniaturized, however, thereby increasing packaging density, some type of defect control technique must necessarily be adopted for improving yield. A known technique for controlling defective bits of the mask ROM is disclosed in, for example, ISSCC (International Solid-State Circuit Conference) Dig. Tech. Papers, February 1989, pp. 128-129, 311. In this paper, a redundancy technique using polycrystalline Si fuse is disclosed.
During the course of developing a new and improved technique using EPROM for redundancy control of defects or altering data stored in semiconductor integrated circuit devices having a memory array of mask ROM or the like, the following problems became evident.
An art using an EPROM (Erasable Programmable Read-Only Memory) of a two-layer gate structure for selecting a redundancy circuit is disclosed in Japanese Laid-Open Patent Publication No. 60-83349. The two-layer gate structure mentioned above is such that it is formed by depositing a gate insulating film, a floating gate electrode formed of a first layer of poly-Si film, an insulating film, and a control gate electrode formed of a second layer of poly-Si film in succession on a semiconductor substrate. In the EPROM, it is required that a predetermined high voltage (around 12V) be applied to the control gate of an EPROM cell for writing information therein. Accordingly, the insulating film must be a thin insulating film having a quality and thickness controlled so as to satisfy required writing/reading characteristics. Therefore, in technology using the EPROM of a two-layer gate structure for the redundancy circuit, it is required that a special fabrication step be added for forming, for example, a highly reliable insulating film to be interposed between the floating gate and the control gate which thereby increases the number of fabrication steps. Known EPROMs of a two-layer gate structure are disclosed, for example, in U.S. Pat. No. 4,918,501 and IEDM (International Electron Device Meeting) Tech. Dig., pp. 631-634, 1985.
Further, a technology using an EPROM of a single-layer polysilicon gate structure is described, for example, in The Transactions of the Institute of Electronics, Information, and Communication Engineers, Vol. 90, No. 47, pp. 51-53, May 21, 1990.
The present inventors have carefully considered data retaining characteristics in connection with the development of their improved EPROM cell (nonvolatile storage element) and, through careful analyses of the relationship between the structure of the element and the data retaining characteristic, they were able to scheme their invention which is directed to a nonvolatile storage element of single-layer gate structure whereby the data retaining characteristic is improved and to a semiconductor integrated circuit device using such storage elements.
An object of the present invention is to provide a semiconductor integrated circuit device comprising nonvolatile storage elements of single-layer gate structure whereby the data retaining characteristics are improved.
Another object of the present invention is to provide a semiconductor integrated circuit device which is easy to fabricate and in which redundancy control of defects, change of functions, and trimming can be reliably achieved.
The above and other objects and novel features of the present invention will be better understood from the following description taken in connection with the accompanying drawings.
A representative aspect of the invention disclosed herein will be briefly described as follows.
A barrier layer is provided for a nonvolatile storage element of single-layer gate structure, which is constructed by arranging a floating gate formed of a conductive layer to partly overlap with a control gate formed of a diffusion layer, such that the barrier layer covers a part or the whole (or entire) surface of the floating gate. Such nonvolatile storage elements are used for redundancy control of defects or change of functions.
By the above described means, radical hydrogen presumed to diffuse from a final passivation film on the surface of the element is captured by the barrier layer, and, accordingly, a collapsing of information charges stored on the floating gate can be prevented. Thereby, with high reliability, redundancy control of defects or change of functions of semiconductor integrated circuit devices can be attained.